NEW YORK (Reuters) - Only half of people in the United States who have ever been infected with hepatitis C get proper testing for the liver-destroying disease, U.S. health officials said on Tuesday.

Proper testing is a two-step process in which people who have antibodies get referred for a second more sophisticated test to detect the virus.

According to the U.S. Centers for Disease Control and Prevention, many people who have taken a blood test showing they have been infected with the virus do not get the necessary follow-up testing indicating whether they still need treatment.

"Complete testing is critical to ensure that those who are infected receive the care and treatment for hepatitis C that they need in order to prevent liver cancer and other serious and potentially deadly health consequences," CDC Director Dr. Thomas Frieden said in a statement.

For its study in the CDC publication Vital Signs, researchers looked at data from eight areas across the nation. Of the hepatitis C cases detected with antibody testing, only 51 percent also included a follow-up test result that identified current infection, meaning they were likely unaware if they were still infected with the virus.

As a result of the findings, the CDC is issuing guidelines urging doctors to do follow-up testing on patients to ensure they get the proper treatment.

Hepatitis C, which is transmitted through the blood, kills more than 15,000 Americans each year, mostly from hepatitis C-related illness, such as cirrhosis and liver cancer.

Although a small number of people who test positive for antibodies to hepatitis C infection can clear the virus on their own, about 80 percent of those who test positive remain infected and can develop significant complications from the disease.

In August, the CDC issued new guidelines recommending that all baby boomers be tested for hepatitis C, citing studies suggesting more than 2 million Americans born between 1945 and 1965 may be infected with the virus.

The agency had previously recommended testing only in individuals with certain known risk factors for the infection. It estimates that around 3.2 million Americans are chronically infected with hepatitis C.

The testing may help people get treatment with newly available therapies that can cure around 75 percent of infections.

The field has attracted broad interest with two new hepatitis C drugs, Incivek from Vertex Pharmaceuticals Inc and Merck & Co's Victrelis.

Companies including Gilead Sciences Inc aim to improve on those medicines with pill-only regimens.